An inclusion complex is a chemical complex formed between two or more compounds, where a first compound (also referred to as a host) has a structure that defines a space into which a molecule of a second compound (also referred to as a guest) fits and non-covalently associates with the first compound. The resulting guest-host complex may be referred to as an inclusion compound, an adduct, or a host molecule. The host molecule may bind the guest molecule reversibly or irreversibly.
Cyclodextrins are host molecules that can form inclusion complexes with a variety of different guest compounds. Cyclodextrins are carbohydrates that may be prepared from hydrolyzed starch by the action of cyclodextrin-glycosyl transferase, an enzyme obtainable from several organisms such as Bacillus macerans or related Bacillus strains. Cyclodextrins have a cyclic malto-oligosaccharide structure with 6 or more alpha-1,4-linked glucose units. The most common cyclodextrins are alpha-cyclodextrin, beta-cyclodextrin, and gamma-cyclodextrin with 6, 7, and 8 linked glucose units, respectively. Under aqueous conditions, cyclodextrins can be topologically represented as toroids (as schematically shown below for gamma-cyclodextrin), with the secondary hydroxyl groups of the smaller opening, and the primary hydroxyl groups of the larger opening, exposed to the surrounding solvent. Because of this topology, the interior of the toroid, while not hydrophobic, is considerably less hydrophilic than the surrounding aqueous environment, and thus is able to host (i.e. bind) hydrophobic molecules such as fats and fatty acids. In contrast, the exterior is sufficiently hydrophilic to impart to cyclodextrins (and their inclusion complexes) substantial water solubility.

Amyloses are also host molecules that can similarly form inclusion complexes with guest compounds. Amylose is one of the two components of starch (the other being amylopectin), and may include several hundred to thousands of glucose subunits. Amylose molecules tend to form helices, with six glucose subunits constituting one complete helical sub-unit. Similar to cyclodextrins, amylose binds fatty acids to form inclusion complexes.